Circulatory air sifter

ABSTRACT

This invention relates to a vertically axised circulatory air sifter having a central sifting chamber for the reception of material to be sifted and an outer annular chamber for fine material separation. A rotary, circulatory fan is disposed above the sifting chamber to establish air circulation through the chambers. At least one cooling air feed inlet communicates with the outer annular chamber and an air outlet communicates with the lower part of the sifter.

United States Patent [191 Henne et a1.

[451 Aug. 26, 1975 1 CIRCULATORY AIR SIFTER [75] Inventors: Heinrich Henne; Norbert Vorloeper,

both of Ennigerloh, Germany [73] Assignee: Polysius AG, Neubeckum, Germany [22] Filed: June 25, 1973 [21] Appl. N0.: 373,016

[30] Foreign Application Priority Data July 21, 1972 Germany n 2235789 [52] US. Cl 209/11; 209/139 A [51] Int. Cl. B07B 7/00 [58] Field of Search 209/11, 139 A, 144, 139 R; 34/57'E; 210/512 [56] References Cited UNITED STATES PATENTS 1,509,915 9/1924 Stcbbins 34/57 E 2,890,764 6/1959 Arnold 209/144 X 3,175,686 3/1965 Ricth 209/3 3,349,548 10/1967 Boyenuu 210/512 X 3,358,844 12/1967 Klein 209/144 X 3,656,618 4/1972 Janich 209/139 A 3,682,302 8/1972 Bermtot 209/139 R 3,734,287 5/1973 lager 209/139 A FOREIGN PATENTS OR APPLICATIONS 1,018,020 1/1966 United Kingdom 209/139 559,977 7/1931 Germany 209/11 219,647 10/1924 United Kingdom 209/139 A 657,452 9/1951 United Kingdom 209/139 A 1,1 12,624 5/1968 United Kingdom.. 34/57 E 1,911,417 9/1970 Germany 209/11 Primary Examiner' R0bert Halper Attorney, Agent, or FirmLearman & McCulloch 5 7 ABSTRACT This invention relates to a vertically axised circulatory air sifter havinga central sifting chamber for the reception of material to be sifted and an outer annular chamber for fine material separation. A rotary, circulatory fan is disposed above the sifting chamber to establish air circulation through the chambers. At least one cooling air feed inlet communicates with the outer annular chamber and an air outlet communicates with the lower part of the Sifter.

6 Claims, 2 Drawing Figures CIRCULATORY AIR SIFTER Circulatory air sifters of the type to which the invention relates are frequently disposed downstream from a grinding plant for mineral material (e.g. cement clinker) so that the material to be sifted often has an undesirably high temperature which can deleteriously affect the quality of the fine material, for example the cement. A number of circulatory air sifters have, therefore, already been developed wherein a certain amount of cooling air is constantly added, with a corresponding amount of the heated circulating air being removed.

Circulatory air sifters are known wherein a cooling air feed pipe terminates in the central sifting chamber. With air sifters of this type it has been found a disadvantage that the cooling air fed into the sifting chamber cools all the ground material, i.e., both the coarse and fine fractions; the cooling effect on the fine material which is to be withdrawn as the final product is, therefore, greatly reduced in unwanted manner, so that this fine material can only be cooled to an inadequate extent. Also the sifting process is unfavorably affected by the supply of cooling air into the central sifting chamher.

In another known circulatory air sifter construction, a number of cooling air inlet apertures are provided in the cover of the sifter housing; cooling air is supplied from above through these apertures into the outer annular chamber (for fine material separation). In order to remove part of the circulatory air from the air sifter, the lower part of the sifter (below a screen through which the circulating air, freed of the fine material, again passes into the shifting chamber) is provided with a further annular chamber, open at its base, from which a corresponding amount of heating circulating air is withdrawn via at least one connecting pipe. Although only the fine material is cooled in this known circulatory air sifter, it has been found in practice that the cyclone-like separation effect in the outer annular chamber, by which the fine material is supposed to be separated from the circulating air current, is considerably deteriorated, so that part of the fine material can be carried back into the interior sifting chamber, which is not desired. Nor does the provision of guide blades in the area of the cooling air inlet aperatures provide any appreciable improvement of the poor separation efficiency. All that really results are higher construction costs.

The invention thus has for its object the provision of a circulatory air sifter of the type initially described, wherein optimum cooling of the fine material only is achieved, without the nature of the cooling air supply causing any reduction in the cyclone separation effect.

According to the invention this object is achieved in that the cooling air feed connection is provided tangentially to the outer housing casing in such manner that the direction of flow of the incoming cooling air is generally the same as the direction of flow of the circulating air occupying the annular chamber. In this way the air needed for cooling can be fed into the fine material separation chamber (outer annular chamber) with relatively little resistance to flow, so that even with a relatively low degree of vacuum an adequate supply of cooling air is ensured, and no additional constructional measures are needed. Thus at any time an optimum cooling can be achieved for the fine material located in the outer annular chamber and to be separated out as finished material. At the same time, however, the nature of the cooling air feed (in the same direction of flow as the circulating air moving generally helically in the annular chamber) reinforces the desired effective and cyclone-line separation of the fine material from the circulatory air stream; by suitable arrangement of the cooling air feed connections it can even be improved, in that the cooling air is fed into the annular chamber at a speed such that the centrifugal force acting on the particles of the fine material to be separated out is increased.

The favorable effect on the cyclone-like separation in the outer annular chamber can be still further increased if the cooling air feed connection, formed as a short pipe, is inclined to the outer housing casing at an angle corresponding in general to the angle of inclination of the circulating air flowing downwards in the outer annular chamber.

Further details of the invention will appear from the following description of an embodiment shown in the drawings, wherein:

FIG. 1 is a schematic vertical section through a circulatory air sifter in accordance with the invention; and

FIG. 2 is a simplified plan view of the air sifter shown in FIG. 1.

The vertically axised circulatory air sifter shown in the drawings includes a central sifting chamber 1 formed by a cylindrical inner housing casing 2 which is joined below to a short conical section 2. In a plane below the sifting chamber is a ring of guide blades 3 which then joins a coarse material collecting hopper 4 with an outlet pipe 4. The inner housing casing 2 separates the central sifting chamber 1 from an outer annular chamber 5 which is used for separation of the fine material. This outer annular chamber 5 is formed by the casing 2 and by the cylindrical casing 6 of the outer sifter housing, which also comprises a generally horizontal upper cover 7 and a fine material hopper 8 adjacent the base of the casing 6, and with an outlet pipe 8 for the fine material.

In the central sifting chamber is a spreader plate 9 adapted to rotate with a central vertical sifter shaft 10 which projects from the top downwards into the sifting chamber 1 and is driven by drive means 1 1 mounted on the housing cover 7. Coaxially with and spaced away 7 from the sifter shaft 10 there is disposed a material supply pipe 12, of funnel shape at its upper part and terminating above the spreader plate 9. The material supply pipe 12 is surrounded by a hollow shaft 13 mounted coaxially with pipe 12 and which is adapted to rotate with the spreader plate 9 and thus with the sifter shaft 10. At the upper part of the shaft 13 is a horizontally disposed air circulating fan 14.

Below a plane which is defined by the central horizontal plane 15 of the fan 14 there are provided two cooling air inlet connections, formed as short pipes l6, 16', to the cylindrical casing 16 of the outer housing. The axis of each cooling air feed connection is disposed substantially tangentially to the outer housing casing 6 and to the annular chamber 5 in such manner that the direction of flow (cf arrow 17) of the incoming cooling air is generally the same as the direction of flow (cf arrow 18) of the circulating air occupying the annular chamber (see FIG. 2). Preferably the two cooling air feed pipes 16, 16' are diametrically opposite each other.

For certain applications (e.g. for the larger type of sifter plant), it may also be desirable to provide more 3 than two cooling air feed connections, uniformly distributed in the peripheral direction round the outer housing casing 6. v

As maybe seen from FIG. 1 the cooling air feed pipes 16, 16' are also disposed on the outer housing casing 6-at an inclination (in the direction of the annular chamber) whose angle a coincides approximately with the inclination of the circulating air flowing downwards in the outer annular chamber (fine material separation chamber); this angle of inclination a can amount to 10 7 In the lower part of the air sifter, ie at the upper rim of the coarse material hopper 4 there is a further downwardly open annular chamber 19 which together with a pipe 20 attached thereto serves to carry away part of the heated circulating air.

7 Material to be sifted is flung into the central sifting chamber via the supply pipe 12 and spreader plate 9. The rotary motion of the shaft 10 at the same time drives the 'circulation fan 14, thereby producing a circulating air stream (of arrow 21) which flows upwards in the sifting chamber 1, through fan 14 outwards into the outer annular chamber 5, through which it passes generally helically downwards. During its upward passage within the sifting chamber 1, the air entrains the fine material from the introduced material and carries Lit in an upward direction into annular chamber 5, wherein under the centrifugal force imposed it is hurled against the inner surface of the wall 6 of the outer housing, in the same manner as in a cyclone, and separated out. The fine material then leaves the sifter through the outlet pipe 8'. The coarse material passes downward along the inner wall of the inner housing casing 2 and the'cone 2 adjacent thereto and is removed via the a coarse material hopper 4 and the outlet pipe 4.

' In order to be able to cool the finished fine material removed from the sifter in optimum manner, cooling air is fed tangentially via pipes 16, 16' into the outer annu-lar chamber 5 (fine material separation chamber) so that in advantageous manner only this fine material is cooled, but not the coarse material. The tangential a'nd slightly downwardly directed entry of the cooling air reinforces the cyclone-like separation effect, so that the fine material can be separated from the air stream particularly effectively.

Depending on the amount of cooling air fed in, an appropriate fraction of the heated circulating air is extracted via the lower annular chamber 19 and the connected pipe 20.

It will be realized that a circulatory air sifter in accordance with the invention may be formed in other ways than in FIGS. 1 and 2. It is also possible to replace the cooling air feed pipes for instance by a type of screen at the periphery of the outer housing casing in order to pass therethrough the necessary cooling air. Finally, it should be stated that, especially for large air sifter constructions, the cooling air feed pipes 16, 16' could also be disposed on the outer housing casing above the plane defined by the horizontal central plane of the fan.

We claim:

1. A vertically axised circulatory air sifter construction comprising an inner cylindrical casing forming a sifting chamber; and outer cylindrical casing enclosing said inner casing and forming with the latter an annular separation chamber; means for introducing to said sift.- ing chamber material to be sifted; for means rotatable in a horizontal plane for establishing a flow of air circumferentially and downwardly through said annular chamber and thence upwardly through said sifting chamber at least one tubular secondary air inlet member having its axis tangential to said annular chamber and opening directly into said annular chamber at a level below the plane of rotation of said fan means for introducing cooling air into said annular chamber in a direction corresponding to the circumferential direction of air fiow through said annular chamber.

2. The construction according to claim 1 wherein a plurality of said inlet members are spaced circumferentially of said outer casing.

3. The construction according to claim 2 wherein there are two of said inlet members diametrically opposed from one another.

4. The construction according to claim 1 wherein said inlet member has its axis inclined downwardly in the direction of said annular chamber.

5. The construction according to claim 4 wherein the inclination of the axis of said tubular member is about 10 l5with respect to the horizontal.

6. The construction according to claim 1 wherein said flow of air through said annular chamber is helical and wherein said air inlet member is inclined to the horizontal at an angle corresponding substantially to the helical pitch of said flow of air.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,901,794 Dated Auqust 26, 1975 lnvennnxs) Heinrich Henne and Norbert Vorloeper It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 16, cancel "and" and insert -an-.

Column 4, line 19, cancel "for" and insert fan.

Signed and Sealed this twen ty-eight D ay Of October 1 9 75 [S AL] Attest:

RUTH C. MASON C. MARSHALL DANN Altesting Officer Commissioner vfPaIents and Trademarks 

1. A VERTICALLY AXISED CIRCULATORY AIR SIFTER CONSTRUCTION COMPRISING AN INNER CYLINDERICAL CASING FORMING A SIFTING CHAMBER, AND OUTER CYLINDERICAL CASING ENCLOSING SAID INNER CASING AND FORMING WITH THE LATTER AN ANNULAR SEPARATION CHAMBER, MEANS FOR INTRODUCING TO SAID SIFTING CHAMBER MATERIAL TO BE SIFTED, FOR MEANS ROTATABLE IN A HORIZONTAL PLANE FOR ESTABLISHING A FLOW OF AIR CIRCUMFERENTIALLY AND DOWNWARDLY THROUGH SAID ANNULAR CHAMBER AND THENCE UPWARDLY THROUGH SAID SIFTING CHAMBER AT LEAST ONE TUBULAR SECONDARY AIR INLET MEMBER HAVING ITS AXIS TANGENTIAL TO SAID ANNULAR CHAMBER AND OPENING DIRECTLY INTO SAID ANNULAR CHAMBER AT A LEVEL BELOW THE PLANE OF ROTATION OF SAID FAN MEANS FOR INTRODUCING COOLING AIR INTO SAID ANNULAR CHAMBER IN A DIRECTION CORRESPONDING TO THE CIRCUMFERENTIAL DIRECTION OFAIR FLOW THROUGH SAID ANNULAR CHAMBER.
 2. The construction according to claim 1 wherein a plurality of said inlet members are spaced circumferentially of said outer casing.
 3. The construction according to claim 2 wherein there are two of said inlet members diametrically opposed from one another.
 4. The construction according to claim 1 wherein said inlet member has its axis inclined downwardly in the direction of said annular chamber.
 5. The construction according to claim 4 wherein the inclination of the axis of said tubular member is about 10* - 15*with respect to the horizontal.
 6. The construction according to claim 1 wherein said flow of air through said annular chamber is helical and wherein said air inlet member is inclined to the horizontal at an angle corresponding substantially to the helical pitch of said flow of air. 